This invention relates generally to spray nozzle configurations and, more particularly, to the configuration and operation of spray nozzles for spraying scale conditioning solution onto a moving strip of heated metal.
Scale conditioning in certain types of alloy steels, such as stainless steel and other types of alloys prior to actual pickling in order to condition the scale for easier removal is well known in the art. One conventional technique for scale conditioning is the use of fused salt baths normally comprised of a caustic, such as sodium hydroxide or potassium hydroxide, or mixtures thereof and preferably some type of oxidizing agent, such as sodium nitrate or potassium nitrate. In this conventional technique, the salt bath is fused and, in one embodiment, the moving strip of material as it emerges from an annealing furnace is submerged in the fused bath, wherein the chemical action of the fused salt conditions the scale and makes it more amenable to removal by a subsequent acid pickling which also is normally done in the line with the salt bath. In some cases, the scale conditioning by the salt bath may be sufficient of itself to remove scale, thus obviating the need for an acid pickle following the scale conditioning. However, in most instances, the acid pickle is required following the scale conditioning. In view of the occasional use of scale conditioning treatment itself for the removal of scale, this scale conditioning treatment is sometimes referred to as salt bath descaling even if followed by an acid pickle. Thus, the terms xe2x80x9cscale conditioningxe2x80x9d and xe2x80x9csalt bath descalingxe2x80x9d are often used interchangeable and synonymously.
While this fused salt bath technique of descaling is very efficient in many instances, it is somewhat expensive in that the bath must be maintained in a fused condition, requiring insulated tanks and heaters to maintain the bath in the fused condition. Moreover, because of drag-out and other factors, the amount of salt required for this scale conditioning is relatively high. Additionally, temperature and chemical resistant tanks are required and temperature and chemical resistant rolls are also required to be immersed in the salt bath to guide the strip therethrough, all adding to the expense of the line. Thus, while salt bath conditioning is an effective way to provide scale conditioning, in some instances the costs make it desirable to seek other techniques.
One technique that has been proposed to replace the fused salt bath is one in which a fused salt is sprayed onto the moving strip of steel as it emerges from the annealing furnace. This does provide some economic benefit. However, there are some drawbacks in certain instances to the spraying of fused salt onto a strip, such as the necessity to maintain the salt in a fused condition which means insulated tanks and energy to maintain the salt fused. Also, the temperature at which the salt is sprayed, together with the composition of the material sprayed tends to degrade the nozzle life for the nozzles being used to spray the fused salt. Such a technique is shown in U.S. Pat. No. 5,272,798, commonly assigned herewith. Other techniques have been developed for spraying salt onto a moving heated strip of material. In patent application Ser. No. 09/469,687, an aqueous solution of caustic material is sprayed onto a moving strip of material as it emerges from an annealing furnace. This application is incorporated herein by reference as if it were fully set forth. This technique has proved very successful over the fused salt bath technique and the technique of spraying of the fused salt onto the surface of the metal. However, as disclosed in that application, the nozzles are all in a relatively fixed position with respect to the strip in the pass line. Thus, if maintenance is required on any of the nozzles, the line must be shut down while such maintenance is performed. In some instances where there are frequent changes in gauge and/or composition and/or width of the material, this is not a significant problem. However, in some instances, it is desired to be able to continue to operate the line while repairing or replacing or doing any necessary maintenance on the nozzles because of the nozzles being clogged or otherwise ineffective, i.e. to service the nozzles without shutting down the line.
According to the present invention, a method and system for spraying scale conditioning aqueous solutions onto opposite sides of a metal strip for scale conditioning is provided. The system includes a housing which defines a chamber through which the moving strip passes on the strip pass line. At least one nozzle maintenance station is provided which is disposed off the strip pass line. A first set of spray nozzles is provided having a first array of nozzles mounted on a first nozzle mounting structure and a second array of nozzles mounted on a second nozzle mounting structure. An actuation mechanism is provided to move the first and second arrays of nozzles between a first position wherein the first array of nozzles is disposed on one side of the strip pass line in a spraying position, and the second array of nozzles is disposed on the opposite side of the strip pass line in a spraying position, and a second position wherein said first and second arrays of said nozzles are disposed at a nozzle maintenance station. A second set of spray nozzles is provided having a third array of nozzles mounted on a third nozzle mounting structure, and a fourth array of nozzles mounted on a fourth nozzle mounting structure, and an actuating mechanism to move said second set of nozzles between a first position, wherein said third array of nozzles is disposed on one side of said strip pass line in a spraying position and spaced from said first array of nozzles, and the fourth array of nozzles is disposed on the opposite side of said strip pass line in a spraying position, spaced from a second array of nozzles; and a second position wherein said third and fourth arrays of nozzles are disposed at a maintenance station.
In another embodiment, the nozzles of the first set can be composed of two separate sections mounted on opposite sides of the strip, with the combined sections covering the width of the strip in the spraying position. In this case, there is a nozzle maintenance station on each side of the strip.
The spraying can be accomplished with only one set of nozzles so, if any nozzle in one set or the other is clogged, that set of nozzles can be removed to the nozzle maintenance station and any work that needs to be done on the nozzle can be accomplished, including the replacement of any nozzle or any group of nozzles. This can be done while the line continues to run and the other set of nozzles is used to spray the solution on both sides of the strip as it continues to pass through the chamber. Preferably, both arrays of nozzles in each set are movable together and, preferably, there is one nozzle maintenance station and, preferably, the nozzle maintenance station is configured so that it can accommodate either set (but not both sets concurrently) of nozzles while the other set is deployed and operating.
The invention also contemplates sensing devices to sense when any given nozzle is not performing according to a preselected standard. In-line activities, such as providing a charge of compressed air to blow out any clogs in the nozzle while it is still deployed, may be provided.
The invention also contemplates providing shaping of the nozzle spray patterns on the strip so as to obtain optimum spray coverage.
The parameters of controlling the composition of the solution being sprayed, the concentration of the solution being sprayed, and the temperature of the strip, are all described in said application Ser. No. 09/469,687 and need not be repeated here, the present invention being related specifically to the spray nozzle configurations used for such spraying.